The present invention relates to a refrigerant cycle apparatus constituted by sequentially connecting a compressor, a gas cooler, throttling means and an evaporator.
In this type of conventional cycle apparatus, a refrigerant cycle (refrigerant circuit) is constituted by sequentially piping and connecting a rotary compressor (compressor), a gas cooler, throttling means (expansion valve or the like), an evaporator and others in an annular form. Further, a refrigerant gas is taken in to a low-pressure chamber side of a cylinder from an intake port of a rotary compression element of the rotary compressor, and a refrigerant gas with a high temperature and a high pressure is obtained by compression performed by operations of a roller and a vane. This gas is then discharged to the gas cooler from a high-pressure chamber side through a discharge port and a discharge sound absorbing chamber. The gas cooler releases heat from the refrigerant gas, then this gas is squeezed by the throttling means and supplied to the evaporator. The refrigerant is evaporated in the evaporator, and a cooling effect is demonstrated by performing the endotherm from the periphery at this time.
Here, in order to cope with global environment problems in recent years, there has been developed an apparatus which utilizes carbon dioxide (CO2) which is a natural refrigerant even in this type of refrigerant cycle without employing conventional fluorocarbon and uses a refrigerant cycle which operates with a high-pressure side as a supercritical pressure.
In such a refrigerant cycle apparatus, in order to prevent a liquid refrigerant from returning into the compressor which results in liquid compression, an accumulator is arranged on a low-pressure side between an outlet side of the evaporator and an intake side of the compressor, the liquid refrigerant is stored in this accumulator, and only the gas is taken into the compressor. Further, throttling means is adjusted so as to prevent the liquid refrigerant in the accumulator from returning to the compressor (see, e.g., Japanese patent Application Laid-open No. 1995/18602).
However, providing the accumulator on the low-pressure side of the refrigerant cycle requires a larger filling quantity of refrigerant. Furthermore, an opening of the throttling means must be reduced in order to avoid return of the liquid, or a capacity of the accumulator must be increased, which results in a reduction in the cooling capability or an increase in an installation space. Thus, in order to eliminate the liquid compression in the compressor without providing such an accumulator, the present applicant tried developing a refrigerant cycle apparatus shown in FIG. 4 of a conventional example.
In FIG. 4, reference numeral 10 denotes an internal intermediate pressure type multistage (two-stage) compressive rotary compressor, and it is constituted of an electric element 14 as a driving element in a sealed vessel 12, and a first rotary compression element 32 and a second rotary compression element 34 which are driven by a rotary shaft 16 of the electric element 14.
A description will be given as to an operation of a refrigerant cycle apparatus in this case. A refrigerant having a low pressure sucked from a refrigerant introducing tube 94 of the compressor 10 is caused to have an intermediate pressure when compressed by the first rotary compression element 32, and then it is discharged into the sealed vessel 12. Thereafter, this refrigerant enters a refrigerant introducing tube 92A, and flows into an intermediate cooling circuit 150A as an auxiliary cooling circuit. This intermediate cooling circuit 150A is provided so as to pass an inter cooler provided in a heat exchanger 154A, and heat radiation is performed there by an air cooling method. Here, heat of the refrigerant having an intermediate pressure is taken by the heat exchanger 154A. Thereafter, the refrigerant is sucked into the second rotary compression element 34 from a refrigerant introducing tube 92B, the second compression is carried out, the refrigerant is turned into a refrigerant gas having a high temperature and a high pressure, and it is discharged to the outside through a refrigerant discharge tube 96.
The refrigerant gas discharged from the refrigerant discharge tube 96 flows into a gas cooler provided in the heat exchanger 154A, heat radiation is performed in the gas cooler by the air cooling method, and this gas then passes through an internal heat exchanger 160. Heat of the refrigerant is taken by a refrigerant on the low-pressure side which has flowed out from an evaporator 157, and this refrigerant is further cooled. Thereafter, the refrigerant is depressurized by an expansion valve 156, and a gas/liquid mixed state is obtained in this process, and then the refrigerant flows into the evaporator 157 where it is evaporated. The refrigerant which has flowed out from the evaporator 157 passes through the internal heat exchanger 160, and it is heated by taking heat from the refrigerant on the high-pressure side in the internal heat exchanger 160.
Moreover, a cycle that the refrigerant heated in the internal heat exchanger 160 is sucked into the first rotary compression element 32 of the rotary compressor 10 from the refrigerant introducing tube 94 is repeated. A degree of superheat can be taken by heating the refrigerant which has flowed out from the evaporator 157 by the internal heat exchanger 160 using the refrigerant on the high-pressure side, return of the liquid that the liquid refrigerant is sucked into the compressor 10 can be assuredly avoided without providing an accumulator or the like on the low-pressure side, and an inconvenience that the compressor 10 is damaged by liquid compression can be eliminated.
Additionally, effective cooling can be performed in the inter cooler of the heat exchanger 154A by passing the refrigerant compressed by the first rotary compression element 32 through the intermediate cooling circuit 150A, thereby improving a compression efficiency of the second rotary compression element 34.
On the other hand, the heat exchanger 154A is constituted of the gas cooler and the inter cooler of the intermediate cooling circuit 150 as described above. A description will now be given as to a structure when, e.g., a micro-tube heat exchanger 154A is used in the refrigerant cycle apparatus with reference to FIG. 5. As shown in FIG. 5, in the heat exchanger 154A, an inter cooler 151A is arranged on the upper side, and a gas cooler 155A is arranged on the lower side. A refrigerant introducing tube 92A connected with the inside of a sealed vessel 12 of a compressor 10 is connected with headers 201 at an inlet of the inter cooler 151A. The headers 201 are connected with ends of respective micro-tubes 204 on one side, and they divide the refrigerant into a plurality of flows which are passed to a plurality of small refrigerant paths formed to the micro-tubes 204. Each of the micro-tubes 204 has a substantial U shape, and a plurality of fins 205 are attached at the U-shaped part. Further, ends of the micro-tubes 204 on the other side are connected with a header 202 at an outlet of the inter cooler 151A, and the refrigerants which have flowed through the respective small refrigerant paths flow into each other here. The header 202 at the outlet is connected with a refrigerant introducing tube 92B connected with a second rotary compression element 34 of the compressor 10.
Furthermore, the refrigerant compressed by the first rotary compression element 32 flows into the headers 201 at the inlet of the inter cooler 151A of the heat exchanger 154A from the refrigerant introducing tube 92A, it is divided into a plurality of flows, these flows enter the small refrigerant paths in the micro-tubes 204, and the refrigerants release heat upon receiving ventilation of a fan 211 at the step that they pass through the small refrigerant paths. Thereafter, the refrigerants flow into each other at the header 202 at the outlet, the refrigerant flows out from the heat exchanger 154A, and it is sucked into the second rotary compression element 34 from the refrigerant introducing tube 92B.
Moreover, a refrigerant discharge tube 96 of the compressor 10 is connected with headers 207 at the inlet of a gas cooler 155a. The headers 207 are connected with the ends of the respective micro-tubes 210 on one side, and divide the refrigerant into a plurality of flows which are caused to pass through small refrigerant paths formed in the micro-tubes 210. Each of the micro-tubes 210 is formed into a meandering shape, and a plurality of fins 205 are disposed to the meandering part. Further, ends of the micro-tubes 201 on the other side are connected to a header 208 at an outlet of the gas cooler 155A, and the refrigerants which have flowed through the respective small refrigerant paths of the micro-tubes 210 flow into each other here. The header 208 at the outlet is connected with a pipe running through the internal heat exchanger 160.
Furthermore, the refrigerant discharged from the second rotary compression element 34 of the compressor 10 flows into headers 207 at an inlet of the gas cooler 155A of the heat exchanger 154 from the refrigerant discharge tube 96, and is divided into a plurality of flows which enter the small refrigerant paths in the micro-tubes 210. The divided refrigerants release heat upon receiving ventilation of a fan 211 in the process of passing through these paths. Thereafter, the refrigerants flow into each other in the header 208 at the outlet. Then, the refrigerant flows out from the heat exchanger 154A and passes through the internal heat exchanger 160.
Constituting the heat exchanger 154A by using the gas cooler 155A and the inter cooler 151A of the internal cooling circuit 150A in this manner does not require separately forming the gas cooler 155A and the inter cooler 151A of the refrigerant cycle apparatus. Therefore, an installation space can be reduced.
In the refrigerant cycle apparatus including the heat exchanger 154A, a ratio in heat radiation capability of the gas cooler 155A of the heat exchanger 154A and the inter cooler 151A must be changed in accordance with use conditions. That is, in cases where the refrigerant cycle apparatus is used as a regular cooling apparatus, it is desired to improve the cooling efficiency (refrigerating efficiency) in the evaporator 157 by effectively cooling the refrigerant gas discharged from the second rotary compression element 34 even if a refrigerant circulating quantity in the refrigerant cycle is large. Therefore, it is necessary to set the heat radiation capability of the gas cooler 155A so as to be relatively high.
On the other hand, in cases where the refrigerant cycle apparatus is used as a cooling apparatus for a super-low temperature by which a temperature of a cooled space becomes not more than −30° C., it is desired to evaporate the refrigerant in a super-low temperature area in the evaporator 157 by suppressing an increase in temperature of the refrigerant gas discharged from the second rotary compression element 34 by increasing a flow path resistance of the expansion valve 156 or improving the heat radiation capability of the refrigerant in the intermediate cooling circuit 150. Therefore, it is necessary to set the head radiation capability of the inter cooler 151A of the intermediate cooling circuit 150 so as to be relatively high.
However, in the conventional heat exchanger 154A, since the micro-tubes 204 and 210 used in the gas cooler 155A in the heat exchanger 154A and the inter cooler 151A have different shapes, the design must be changed each time. Therefore, there is generated a problem of an increase in manufacturing cost.